1. Field of the Invention
The present invention generally relates to a filter for a centrifugal separator, and more particularly, to a filter for filtrating the example, a biological substance such as an antibody, enzyme, nucleic acid and protein, for the purpose of concentration, desalting, purification, fractionation, etc. thereof.
2. Description of the Prior Art
Conventionally, the filter of a type which is utilized in association with the centrifugal separator is well known. The centrifugal separator can be classified as two types, namely a so-called swing rotor type and a so-called angle rotor type. The swing rotor type of centrifugal separator has a rotor for pivotally suspending a plurality of filters therearound so that the filters can swing so as to become horizontal when the rotor rotates. Contrary to the above, the angle rotor type of centrifugal separator comprises a rotor having a plurality of bores for accommodating the filters. Each of the bores is formed such that the axis of each bore is inclined to the rotational axis of the rotor at a predetermined angle, for example 30.degree. to 60.degree..
Meanwhile, the angle rotor type of centrifugal separator has advantages in that the filters can be fixedly accommodated in the bores formed in the rotor in a stable manner even if the rotor rotates at a very high speed, and the filtration speed is relatively high.
An example of the prior art filter f is shown in FIGS. 1 to 3. The filter f has a cylindrical configuration comprising a cylindrical sample container 1, into which a liquid sample is to be supplied, and a cylindrical filtrate container 3 which is coupled to the bottom portion of the sample container and in which the filtrate is reserved. A filter film 2 is positioned between the pair of containers 1 and 3 and is generally arranged on a bottom wall of the sample container 1. It is to be noted that, as apparent from the drawing, the filter film 2 is positioned at the right angle with respect to an axis O' of the cylindrical filter f.
FIG. 2 shows a case where the filter f as described above is utilized for the angle rotor type of centrifugal separator. The rotational axis of the rotor is indicated by a symbol "O". Each filter f is fixed in the corresponding bores of the rotor so that the axis O' of each filter f is inclined at an angle .theta.1 with respect to the axis O. When the rotor rotates in a direction indicated by an arrow P1 in FIG. 2, a centrifugal force in a direction indicated by an arrow V is generated. Meanwhile, since the axis O' of the filter f is inclined to the axis O of the rotor at the angle .theta.1, the filter film 2 is inclined to the axis O at an angle .theta.2, provided that .theta.2=90.degree.-.theta.1. Accordingly, the residue or solute 4b contained in the liquid sample 4 gradually moves to the left as viewed in FIG. 2, due to the centrifugal force according to the proceeding of the operation to separate from the solvent 4a. In this case, although the residue 4b is depressed onto the filter film 2, the residue 4b is able to slide on the filter film 2 in the direction V of the centrifugal force since the filter film 2 is inclined to the axis O at the angle .theta.2. That is to say, some part 2a of the filter film 2 near to the axis O is free from the covering of the residue 4b even if the centrifugal separation has sufficiently proceeded. Thus, the part 2a of the filter film 2 is prevented from being clogged with the residue 4b, so that the solvent 4a is able to readily pass through the part 2a of the filter film 2 from the sample chamber of the sample container into the filtrate chamber of the filtrate container 3. It will be apparent from the foregoing description that, according to the angle rotor type of the centrifugal separator, the high filtration speed of the filter film 2 can be maintained for a long period of time.
When the filter f is utilized with the swing rotor type of centrifugal separator, the filtration speed of the filter film 2 decreases rapidly according to operation. FIG. 3 shows a case where the filter f is adapted to the swing rotor type of centrifugal separator. As shown in FIG. 3, the residue 4b gradually moves in the direction V of the centrifugal force according to the operation. In this case, the filter 2 is positioned parallel to the axis O of the rotor during the operation. Accordingly, the residue 4b rapidly covers the entire filter film 2. When the layer of the residue become relatively thick, the entire filter film 2 is clogged with the residue 4b so that the filtration speed of the filter film 2 rapidly decreases resulting in the consumption of the operation time.
Needless to say, the high filtration speed of the filter of the type as described above should be maintained for a long period of operation time when the filter is adapted to the swing rotor type of centrifugal separator as well as the angle rotor type of centrifugal separator.